Who is this mysterious masked man with a metal arm and one seriously dangerous gun? As it says at the top of this latest character poster from the upcoming Captain America sequel, this is The Winter Soldier, the insanely dangerous, highly skilled assassin who serves as the primary antagonist in the film's plot. What you may not know, however, is that he is a character with a very dark secret that ties him directly to the history of the titular Marvel hero.

The Winter Soldier is being played by Sebastian Stan, whose name you likely recognize for playing Bucky Barnes in Joe Johnston's Captain America: The First Avenger. The last we saw his character, he was plummeting down to what we assumed was certain death after being knocked out of a moving train moving along the side of a cliff. Bucky didn't die, however, and instead was found and turned into the murderous agent you see in action here:

Comic book fans are very familiar with the Winter Soldier storyline, as its one of the most famous arcs in Captain America comics, but I'm very curious as to how they will treat the character in the film as a result. Will the Winter Soldier's real identity be kept as a third act reveal, or will it be something that we know about from the very start of the story? I'm really hoping its the latter, as it would not only make for a better viewing experience for the movie's core fan base, but would also make for a more interesting and creative narrative.

Based on a script written by Christopher Markus and Stephen McFeeley - the same scribes behind both the first Captain America and Thor: The Dark World - this new adventure in the Marvel Cinematic Universe finds its eponymous superhero still trying to adjust to life in the modern world, working alongside Black Widow (Scarlett Johansson) as a field operative for S.H.I.E.L.D. What he doesn't know is that there is a very real danger looming on the horizon, and soon he becomes to question whether or not he is fighting for the right team. Anthony Mackie, Cobie Smulders, Frank Grillo, Emily VanCamp, Hayley Atwell, Robert Redford and Samuel L. Jackson co-star in the blockbuster, which out in theaters in less than a month on April 4th. For now, enjoy all the previously released character posters below: